This invention relates to systems for the protection of secure areas and to intruder detection systems. Specifically, it relates to radar ranging type systems that are adapted to surveillance of the air space over the perimeter of the secure area and that include instrumentation for unambiguous range and altitude measurements.
It is often necessary to protect equipment and secure areas from unauthorized, unwanted and sometimes hostile personnel and vehicles. Such protection conventionally includes fencing that encompasses the area or equipment to be protected. Intruder detection systems are also used in conjunction with fences or other physical deterrent barriers to enable responsible personnel to monitor the premises and to take appropriate action in response to detected intrusions. One well known state-of-the-art intrusion detection system utilizes radar ranging principles. This type of system is implemented by means of leaky transmission lines that encompass the secure area. Violation by an intruder of the r.f. field that radiates from the leaky transmission line results in reflections which can be processed in a known manner to identify and locate any given intrusion event. Surveillance of the air space over the perimeter of the secure area is also accomplished by using an upward looking sensor in conjunction with a leaky transmission line. This directs the distributed r.f. energy transmitted through the leaky transmission line upward, thus providing an electronic "fence" any violation of which results in reflections that are detected and processed by system processing circuits for the activation of alarms and displays. Although systems utilizing these principles expand the surveillance to include the air space over the secure area the state-of-the-art timing techniques used with such systems are inadequate to provide exact intruder location information. That is, only total distance from system transmitter/receiver location to the intrusion is measured providing the knowledge that an intrusion event has occurred while giving no information as to exactly where it has occurred. Therefore an ambiguity exists as to whether the intrusion has occurred at a close high altitude location or at a remote low altitude location or at some intermediate location.
There currently exists the need therefore for instrumentation that will eliminate the location ambiguities that surveillance systems of the type described are subject to. The present invention is directed toward satisfying that need.